In many systems there is a need to continuously apply a uniform coating of a coating material onto a surface. An example of such a system is an electrophoretic imaging system, as described in detail in U.S. Pat. Nos. 3,384,565; 3,384,566 and 3,383,993, all granted on May 21, 1968. In such an imaging system, variously colored light absorbing particles are suspended in a non-conductive liquid carrier. The suspension is placed between electrodes, subjected to a potential difference and exposed to an image. As these steps are completed, selected particle migration takes place in image configuration, providing a visible image on one or both of the electrodes. An essential component of the suspended particles must be photosensitive and apparently undergoes a net change in charge polarity upon exposure to activating electromagnetic radiation, through interaction with one of the electrodes. In a monochromatic system, particles of a single color are used, producing a single colored image equivalent to conventional black-and-white photography. In a polychromatic system, the images are produced in natural color because mixtures of particles of two or more different colors, which are each primarily sensitive to light of a specific wave-length or narrow range of wave-lengths, are used. Particles used in this system must have both intense and pure colors and be highly photosensitive.
Ordinarily, electrophoretic imaging systems include a transparent, conductive injecting electrode upon which the dispersion of photosensitive particles in an insulating liquid is coated. The image to be reproduced is projected on the suspension on the injecting electrode. During exposure, a potential, usually of from 300 to 3,000 volts is imposed on the suspension between the injecting electrode and a relatively insulating blocking electrode. This blocking electrode, ordinarily in the form of a roller or an endless belt or web, consists of a conductive core with an insulating surface. This blocking electrode is passed across the surface of the liquid suspension during exposure. Unwanted photosensitive particles migrate to the surface of the blocking electrode, leaving an image on the injecting electrode corresponding to the original.
In the use of the above process in a continuous imaging machine, there is a need to uniformly provide the layers of the imaging suspension to one of the electrodes in order to form the best images.